Communication systems that utilize coded communication signals are known in the art. One such system is a direct sequence code division multiple access (DS-CDMA) cellular communication system, such as set forth in the Telecommunications Industry Association Interim Standard 95A (TIA/EIA IS-95A) herein after referred to as IS-95A. In accordance with IS-95A, the coded communication signals used in the DS-CDMA system comprise signals that are transmitted in a common 1.25 MHz bandwidth, hence, spread-spectrum, to base sites of the system from communication units, such as mobile or portable radiotelephones, that are communicating in the coverage areas of the base sites.
Communication systems that utilize coded communication signals are known to employ channel power control methods which control transmission energy of mobile communication units. Reverse-link (mobile communication unit to base site), power control varies the power transmitted by the mobile communication unit to ensure that the power from each mobile communication unit arrives at the base site at the minimum possible power level. If the mobile communication units' transmit power is too low, voice quality will be degraded. If the mobile communication units' power is too high, the mobile communication unit may have high quality voice, but because each mobile communication unit's signal in a spread-spectrum system is typically transmitted on the same frequency, the resulting excess interference will degrade the overall system capacity. The magnitude of noise, which is inversely proportional to bit energy per noise density i.e., Eb/No which is defined as the ratio of energy per information-bit to noise-spectral density, is directly related to the received signal power of each of the other mobile communication units' transmissions. Thus it is beneficial for a mobile communication unit to transmit at the lowest power level possible while maintaining the integrity of the signal, the integrity characterized by its frame erasure rate (FER).
It is also desirable to dynamically adjust the power of all mobile communication units in such a way that their transmissions are received by the base station with substantially the same power level. To accomplish this, it is necessary for the closest transmitters to reduce their power by as much as 80 dB when compared to the power of the furthest transmitters.
The current method of controlling reverse channel power in a CDMA communication system is described in Cellular System Remote Unit Base Station Compatibility Standard of the Electronic Industry Association Interim Standard 95A (TIA/IS-95A). As described in TIA/IS-95A, a power-control group is transmitted from the mobile communication unit and received by the base station. The base station compares the energy of the power-control group to a setpoint threshold and instructs the mobile communication unit to power up or down accordingly via transmitting a power adjustment command to the mobile communication unit. Under nominal conditions, utilizing such a closed loop power control method will result in a setpoint threshold which maintains the Eb/No of the received signal at a substantially fixed level. However, under varying conditions, for example, when a mobile station is moving at varying speeds, different Eb/No are required for a given FER. Thus maintaining a fixed Eb/No may result in different FERs for mobile stations under different conditions.
Therefore, a need exists for a method and apparatus for adjusting a power control setpoint threshold in a wireless communication system which adjusts the power level needs of the mobile communication system while decreasing the period of time over which the threshold adjustments occurs.